Some video game devices and digital televisions of recent years are equipped with a viewer function or a slideshow function. By using these functions, users are able to display still/moving pictures filmed by their digital cameras on a display screen. Still/moving pictures in particular can be provided with various visual effects when combined with CG images. For example, a list of thumbnail images of still/moving pictures can be displayed on a screen, so as to prompt a user to select one of the still/moving pictures by using a graphics user interface (GUI). Following the user's selection, switching from the screen on which the list of the thumbnail images are displayed to a screen on which the selected still/moving picture is displayed can be represented by animation with CG images. Combining still/moving pictures and CG images as above provides entertainment to the user making the user operation, while improving operability of the GUI.
A still/moving picture is combined with a CG image as follows. To start with, a CG image called “object” is represented by an assembly of various graphics, such as a dot, a line, and a polygon. These object graphics may be represented either as images depicted on a two-dimensional (i.e. 2D) plane or as images residing in three-dimensional (i.e. 3D) virtual space. Next, a two-dimensional image (i.e. a texture) representing one frame constituting the still/moving picture is projected onto the object. This operation is called “mapping”. When the object is represented as an image residing in 3D virtual space, “monoscopic images” of the object seen from a certain viewpoint, in other words, images of the object projected onto planes located between the object and the viewpoint, are additionally calculated. The monoscopic images thus obtained by combining the one frame constituting the still/moving picture with the object are displayed on a display screen. By deforming or displacing the object on the 2D plane or in 3D virtual space, the still/moving picture displayed on the surface of the object is also deformed or displaced accordingly.
Meanwhile, in recent years, more and more digital cameras and digital televisions equipped with a stereoscopic image display function are becoming popular in ordinary houses. A “stereoscopic image” denotes a combination of a left-view image and a right-view image which collectively represent one scene stereoscopically viewed by a viewer. The “left-view image” denotes a monoscopic image seen by the left eye of the viewer, and the “right-view image” denotes a monoscopic image seen by the right eye of the viewer. Between the left-view image and the right-view image, there is a difference due to binocular parallax of the viewer. As one method for displaying stereoscopic images, a “frame sequential method” is commonly used. In the frame sequential method, a left-view image and a right-view image are alternately displayed on a display screen. The viewer sees the images through a pair of shutter glasses. The shutter glasses make only the left eye lens transparent when the left-view image is displayed and make only the right eye lens transparent when the right-view image is displayed. As a result, the left-view image is shown only to the left eye of the viewer, while the right-view image is shown only to the right eye. This makes the viewer to perceive the difference between the left-view image and the right-view image as the binocular parallax for a single scene, and thus the two monoscopic images appear to be a single stereoscopic image.
In order to film a stereoscopic image of a real object, it is only necessary to place two digital cameras side by side to resemble the left eye and the right eye of the viewer, and film the object by these cameras at the same time. A technique for converting CG images into a stereoscopic image is also known. For example, Patent Literature 1 discloses a technique for generating a left-view image and a right-view image of an object by displacing a display position of the object on the 2D screen. The above techniques for representing still/moving pictures and CG images as stereoscopic images are expected to be applied to the aforementioned viewer function and slideshow function. It is hoped that using the stereoscopic images will give the viewer a sense of presence that is not available with monoscopic images, while exploring possibilities for a new form of visual effects.